In order to transfer energy from a turbine engine, a conventional combustion engine, an electric motor or any power generating apparatus to a machine to power the machine, it is typically necessary to join the power generating apparatus to the machine with some sort of coupling means. These apparatuses typically transmit power through an angularly rotating shaft and this power output is typically referred to as torque. The power coupling means is a critical piece of equipment since its failure will typically result in the de-energization of the machine.
When a power generating apparatus having a high horsepower output (e.g. a 1,000 H.P. electric motor) is coupled to a machine having a high angular velocity shaft (e.g., a centrifugal pump), it is critical that the shafts of the devices are aligned as closely as possible. Misalignment will result in a number of problems including adverse vibration levels, premature bearing failure, structural damage, overheating, excessive noise, and high wear rate and failure rate of the coupling. Although it is theoretically possible to perfectly align the shafts of the power generating apparatus and the machine, there are practical limitations including measurement equipment, equipment location, adverse environmental factors, differential rates of thermal expansion during operation, etc. In addition, the design may require a specified amount of articulation. There are couplings in the prior art which permit slight shaft misalignment for high torque, high speed applications, however, the amount of misalignment is typically about 1/2.degree. or less and these couplings are typically of metal construction and very heavy. The primary limitation of the power couplings of the prior art is that the materials of construction do not permit high torque and high angular velocity with large shaft misalignment, up to about 10.degree., across a broad temperature spectrum. Such a power coupling must act as a torque transmitting or driving means, and, it must also act as a flexure to permit elastic deformation to compensate for the misalignment.
The power coupling means is particularly crucial in rotary wing aircraft or helicopters. The power coupling means used in helicopters to transfer torque from the power shaft to the helicopter blades is typically referred to as a rotary hub. The rotary hubs of the prior art were complex, metal mechanisms. The disadvantages of these metal rotary hubs were several including weight, fatigue failure, very high maintenance and cost.
There is a constant search in this art to replace metal aircraft parts with lightweight, high strength, fatigue resistant composite components. An example of a helicopter gimbal rotor hub utilizing composite materials is contained in U.S. Pat. No. 4,323,332 which is incorporated by reference.
The elimination of conventional roller bearings and ball bearings in the rotor hub of a helicopter is accomplished in a composite gimbal rotor hub by utilizing composite materials in the blade and hub which are capable of bending and rotating to accommodate blade pitch, flap and lead-lag motion. The rotor hub restrains the blades against centrifugal force and transmits lifting force from the blades to the shaft and airframe of the helicopter. Since the rotary hub should tilt about the central axis of the shaft in a gimbal hub design, it is necessary to provide a tiltable or articulable means for transferring torque from the shaft to the rotor blades. The torque drive structure must be rigid enough to transmit torque directly from the shaft to the helicopter without buckling blades but yet must be sufficiently flexible and bendable to tilt up to approximately 10.degree. from horizontal while transmitting the torque load.
Buckling of a torque drive structure is observed as a wave or series of waves induced in the structure in reaction to a torque load on the structure. Buckling is inherent in a flexible torque drive structure and is undesirable in that it is directly related to reduced fatigue life, reduced torque load capacity and dynamic instability of the torque drive structure. The typical power output to a helicopter hub assembly is in excess of 1,000 H.P. Conventional metal materials do not have the properties required to simultaneously perform the torque driving function and flexure function without buckling and/or structural failure.
Accordingly, what is needed in this art is a flexible composite torque transfer means and a method of manufacturing such a torque transfer means that overcomes the problems of the prior art.